Basic control mechanisms by which rates of protein synthesis and degradation are modified in lung tissue are being investigated in rat lungs perfused in situ. The role of hormones, amino acids, and other substrates, as well as physiological parameters such as ventilatory rate, tidal volume, and blood flow in the control of these pathways, is being evaluated. Furthermore, the extent to which alterations in synthetic or degradative rates contribute to rapid lung growth following pneumonectomy or to loss of lung tissue during starvation is under investigation. During the course of these studies, turnover rates of specific lung proteins will be evaluated, especially those proteins known to be of importance in maintenance of normal lung structure and function.